Refactor unix domain socket store config (#11109)

Following what is outlined in #10766 refactor the uds-remote-store such
that the member variables (state) don't live in the store itself but in
the config object.

Additionally, the config object includes a new necessary constructor
that takes a scheme & authority.

Tests are commented out because of linking errors with the current config system.
When there is a new config system we can reenable them.

Co-authored-by: John Ericson <John.Ericson@Obsidian.Systems>

tests/unit/libstore/ssh-store.cc

@@ -1,6 +1,9 @@
-#include <gtest/gtest.h>
+// FIXME: Odd failures for templates that are causing the PR to break
+// for now with discussion with @Ericson2314 to comment out.
+#if 0
+#  include <gtest/gtest.h>
 
-#include "ssh-store.hh"
+#  include "ssh-store.hh"
 
 namespace nix {
 
@@ -15,7 +18,9 @@ TEST(SSHStore, constructConfig)
                 // TODO #11106, no more split on space
                 "foo bar",
             },
-        }};
+        },
+    };
+
     EXPECT_EQ(
         config.remoteProgram.get(),
         (Strings{
@@ -23,4 +28,28 @@ TEST(SSHStore, constructConfig)
             "bar",
         }));
 }
+
+TEST(MountedSSHStore, constructConfig)
+{
+    MountedSSHStoreConfig config{
+        "mounted-ssh",
+        "localhost",
+        StoreConfig::Params{
+            {
+                "remote-program",
+                // TODO #11106, no more split on space
+                "foo bar",
+            },
+        },
+    };
+
+    EXPECT_EQ(
+        config.remoteProgram.get(),
+        (Strings{
+            "foo",
+            "bar",
+        }));
 }
+
+}
+#endif